Audio signal compression and decompression utilizing amplitude, frequency, and time information

An audio signal is compressed and decompressed. The audio signal is sampled per regular sampling interval to obtain sampled values. The sampled values are orthogonal-transformed per constant period to obtain sequential orthogonal transfer functions. Feature points are extracted that represent change in coefficient intensity of the orthogonal transfer functions per constant frequency interval. Coefficient intensity data, frequency data, and time data of the feature points are obtained. The orthogonal transfer functions are reproduced by interpolating the coefficient intensity of the orthogonal transfer functions on the basis of the coefficient intensity data, frequency data, and time data. The reproduced orthogonal transfer functions are inverse orthogonal-transformed to reproduce the sampled values. And, the reproduced sampled values are converted into the audio signal.